Support disabled state for semantics (#13877)

Fixes https://github.com/flutter/flutter/issues/11993

bin/internal/engine.version

-43327730a27344f1d45a1f9e4d53b14260778ce5
+12e0e38a8b7a30a0d7e83b761c714a901b78f72e

packages/flutter/lib/src/material/list_tile.dart

@@ -453,6 +453,7 @@ class ListTile extends StatelessWidget {
       onLongPress: enabled ? onLongPress : null,
       child: new Semantics(
         selected: selected,
+        enabled: enabled,
         child: new ConstrainedBox(
           constraints: new BoxConstraints(minHeight: tileHeight),
           child: new Padding(

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -2818,6 +2818,7 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     RenderBox child,
     bool container: false,
     bool explicitChildNodes,
+    bool enabled,
     bool checked,
     bool selected,
     bool button,
@@ -2840,6 +2841,7 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
   }) : assert(container != null),
        _container = container,
        _explicitChildNodes = explicitChildNodes,
+       _enabled = enabled,
        _checked = checked,
        _selected = selected,
        _button = button,
@@ -2911,6 +2913,17 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     markNeedsSemanticsUpdate();
   }
 
+  /// If non-null, sets the [SemanticsNode.hasEnabledState] semantic to true and
+  /// the [SemanticsNode.isEnabled] semantic to the given value.
+  bool get enabled => _enabled;
+  bool _enabled;
+  set enabled(bool value) {
+    if (enabled == value)
+      return;
+    _enabled = value;
+    markNeedsSemanticsUpdate();
+  }
+
   /// If non-null, sets the [SemanticsNode.isSelected] semantic to the given
   /// value.
   bool get selected => _selected;
@@ -3213,6 +3226,8 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     config.isSemanticBoundary = container;
     config.explicitChildNodes = explicitChildNodes;
 
+    if (enabled != null)
+      config.isEnabled = enabled;
     if (checked != null)
       config.isChecked = checked;
     if (selected != null)

packages/flutter/lib/src/semantics/semantics.dart

@@ -243,6 +243,7 @@ class SemanticsProperties extends DiagnosticableTree {
   ///
   /// The [container] argument must not be null.
   const SemanticsProperties({
+    this.enabled,
     this.checked,
     this.selected,
     this.button,
@@ -264,6 +265,14 @@ class SemanticsProperties extends DiagnosticableTree {
     this.onMoveCursorBackwardByCharacter,
   });
 
+  /// If non-null, indicates that this subtree represents something that can be
+  /// in an enabled or disabled state.
+  ///
+  /// For example, a button that a user can currently interact with would set
+  /// this field to true. A button that currently does not respond to user
+  /// interactions would set this field to false.
+  final bool enabled;
+
   /// If non-null, indicates that this subtree represents a checkbox
   /// or similar widget with a "checked" state, and what its current
   /// state is.
@@ -1080,6 +1089,8 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
     }
     final List<String> actions = _actions.keys.map((SemanticsAction action) => describeEnum(action)).toList()..sort();
     properties.add(new IterableProperty<String>('actions', actions, ifEmpty: null));
+    if (_hasFlag(SemanticsFlags.hasEnabledState))
+      properties.add(new FlagProperty('isEnabled', value: _hasFlag(SemanticsFlags.isEnabled), ifFalse: 'disabled'));
     if (_hasFlag(SemanticsFlags.hasCheckedState))
       properties.add(new FlagProperty('isChecked', value: _hasFlag(SemanticsFlags.isChecked), ifTrue: 'checked', ifFalse: 'unchecked'));
     properties.add(new FlagProperty('isSelected', value: _hasFlag(SemanticsFlags.isSelected), ifTrue: 'selected'));
@@ -1741,12 +1752,32 @@ class SemanticsConfiguration {
     _setFlag(SemanticsFlags.isSelected, value);
   }
 
+  /// Whether the owning [RenderObject] is currently enabled.
+  ///
+  /// A disabled object does not respond to user interactions. Only objects that
+  /// usually respond to user interactions, but which currently do not (like a
+  /// disabled button) should be marked as disabled.
+  ///
+  /// The setter should not be called for objects (like static text) that never
+  /// respond to user interactions.
+  ///
+  /// The getter will return null if the owning [RenderObject] doesn't support
+  /// the concept of being enabled/disabled.
+  bool get isEnabled => _hasFlag(SemanticsFlags.hasEnabledState) ? _hasFlag(SemanticsFlags.isEnabled) : null;
+  set isEnabled(bool value) {
+    _setFlag(SemanticsFlags.hasEnabledState, true);
+    _setFlag(SemanticsFlags.isEnabled, value);
+  }
+
   /// If this node has Boolean state that can be controlled by the user, whether
   /// that state is on or off, corresponding to true and false, respectively.
   ///
-  /// Do not set this to any value if the owning [RenderObject] doesn't have
-  /// Booleans state that can be controlled by the user.
-  bool get isChecked => _hasFlag(SemanticsFlags.hasCheckedState) && _hasFlag(SemanticsFlags.isChecked);
+  /// Do not call the setter for this field if the owning [RenderObject] doesn't
+  /// have checked/unchecked state that can be controlled by the user.
+  ///
+  /// The getter returns null if the owning [RenderObject] does not have
+  /// checked/unchecked state.
+  bool get isChecked => _hasFlag(SemanticsFlags.hasCheckedState) ? _hasFlag(SemanticsFlags.isChecked) : null;
   set isChecked(bool value) {
     _setFlag(SemanticsFlags.hasCheckedState, true);
     _setFlag(SemanticsFlags.isChecked, value);

packages/flutter/lib/src/widgets/basic.dart

@@ -4764,6 +4764,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     Widget child,
     bool container: false,
     bool explicitChildNodes: false,
+    bool enabled,
     bool checked,
     bool selected,
     bool button,
@@ -4789,6 +4790,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     container: container,
     explicitChildNodes: explicitChildNodes,
     properties: new SemanticsProperties(
+      enabled: enabled,
       checked: checked,
       selected: selected,
       button: button,
@@ -4856,6 +4858,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     return new RenderSemanticsAnnotations(
       container: container,
       explicitChildNodes: explicitChildNodes,
+      enabled: properties.enabled,
       checked: properties.checked,
       selected: properties.selected,
       button: properties.button,
@@ -4895,6 +4898,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     renderObject
       ..container = container
       ..explicitChildNodes = explicitChildNodes
+      ..enabled = properties.enabled
       ..checked = properties.checked
       ..selected = properties.selected
       ..label = properties.label

packages/flutter/test/material/control_list_tile_test.dart

@@ -101,7 +101,12 @@ void main() {
           id: 1,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: null,
-          flags: SemanticsFlags.hasCheckedState.index | SemanticsFlags.isChecked.index,
+          flags: <SemanticsFlags>[
+            SemanticsFlags.hasCheckedState,
+            SemanticsFlags.isChecked,
+            SemanticsFlags.hasEnabledState,
+            SemanticsFlags.isEnabled
+          ],
           actions: SemanticsAction.tap.index,
           label: 'aaa\nAAA',
         ),
@@ -109,7 +114,12 @@ void main() {
           id: 4,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 56.0, 0.0),
-          flags: SemanticsFlags.hasCheckedState.index | SemanticsFlags.isChecked.index,
+          flags: <SemanticsFlags>[
+            SemanticsFlags.hasCheckedState,
+            SemanticsFlags.isChecked,
+            SemanticsFlags.hasEnabledState,
+            SemanticsFlags.isEnabled
+          ],
           actions: SemanticsAction.tap.index,
           label: 'bbb\nBBB',
         ),
@@ -117,7 +127,11 @@ void main() {
           id: 7,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 112.0, 0.0),
-          flags: SemanticsFlags.hasCheckedState.index,
+          flags: <SemanticsFlags>[
+            SemanticsFlags.hasCheckedState,
+            SemanticsFlags.hasEnabledState,
+            SemanticsFlags.isEnabled
+          ],
           actions: SemanticsAction.tap.index,
           label: 'CCC\nccc',
         ),

packages/flutter/test/material/list_tile_test.dart

@@ -347,6 +347,7 @@ void main() {
                 ),
                 const ListTile(
                   title: const Text('three'),
+                  enabled: false,
                 ),
               ],
             ),
@@ -360,13 +361,24 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             label: 'one',
+            flags: <SemanticsFlags>[
+              SemanticsFlags.hasEnabledState,
+              SemanticsFlags.isEnabled,
+            ],
           ),
           new TestSemantics.rootChild(
             label: 'two',
-            flags: <SemanticsFlags>[SemanticsFlags.isSelected],
+            flags: <SemanticsFlags>[
+              SemanticsFlags.isSelected,
+              SemanticsFlags.hasEnabledState,
+              SemanticsFlags.isEnabled,
+            ],
           ),
           new TestSemantics.rootChild(
             label: 'three',
+            flags: <SemanticsFlags>[
+              SemanticsFlags.hasEnabledState,
+            ],
           ),
         ]
       ),

packages/flutter/test/semantics/semantics_test.dart

@@ -246,7 +246,8 @@ void main() {
     expect(config.isSemanticBoundary, isFalse);
     expect(config.isButton, isFalse);
     expect(config.isMergingSemanticsOfDescendants, isFalse);
-    expect(config.isChecked, isFalse);
+    expect(config.isEnabled, null);
+    expect(config.isChecked, null);
     expect(config.isSelected, isFalse);
     expect(config.isBlockingSemanticsOfPreviouslyPaintedNodes, isFalse);
     expect(config.isFocused, isFalse);
@@ -268,6 +269,7 @@ void main() {
     config.isSemanticBoundary = true;
     config.isButton = true;
     config.isMergingSemanticsOfDescendants = true;
+    config.isEnabled = true;
     config.isChecked = true;
     config.isSelected = true;
     config.isBlockingSemanticsOfPreviouslyPaintedNodes = true;
@@ -302,6 +304,7 @@ void main() {
     expect(config.isSemanticBoundary, isTrue);
     expect(config.isButton, isTrue);
     expect(config.isMergingSemanticsOfDescendants, isTrue);
+    expect(config.isEnabled, isTrue);
     expect(config.isChecked, isTrue);
     expect(config.isSelected, isTrue);
     expect(config.isBlockingSemanticsOfPreviouslyPaintedNodes, isTrue);